Inductor type furnace



May 12, 1931. E. F. NORTHRUP INDUCTOH TYPE FURNACE Filed Aug. .2, 192e lParenteel May 12,1931

UNITED STATES;4

liivrarrrlv OFFICE Enwnr FITCH NOnTnnUn-or PRINCETON, NEW JERSEY, AssIGNOB To AJAX ELEC- .Tnornmrc CORPORATION, or TEENTON, NEW JERSEY, A CORPORATION or NEW JERSEY- INDUCTOB TYPE I'UBNAGE Appuuauon mea August 192s. serial om. 296,937. y'

. I v Myl invention relates to electric furnaces of the pool-surrounding inductor type.

The main purpose of my inventonis to reduce the inductor coil heat losses, improvl ing the eiiiciency of operation of the coll. A further purpose is` to improve the eiliciency of a furnace coil which vextends below the furnace charge.

A. further purpose is to obtain a maximum l lbenefit from a coil surrounding and depending below a furnace pool.

Further purposes will appear in the specication and in the claims.

My invention relates to methods involved and'to apparatus by which the methods may be carried out.

I prefer to illustrate a few forms only amon various forms in which my invention may e embodied, selecting forms which are practical, efficient and deslrable, .and which at the same timewell illustrate the principles involved. j

Figures 1-3 are vertical( central sections, largelyv diagrammatic, showing several forms of my' invention. g v

Fi re 2ais a fragmentary section correspon g to part of igure 3 but showing-a different winding. -f f f l In the. drawings similar numerals lindicate like parts. A

Aconsiderable part of the energy in operation of electric furnaces ofthe char e-'surrounding inductor type 1s dissipated inheat within the'inductor coil. This may be reduced for the'same number of coil turns by-enlarging they cross-section of the turns. However, since radial width of individual turns cannot be' increased` to advantage from standpoints of conductivity belcause of the fact that the current through the inductor is largely concentrated along the radially interior portion of the inductor, the increase of the cross-section must be parallel to the axis, increasing the axial length of each turn and of the coil.

.There is alsovof Course some limit to the extension of the axial length of the. coil which may be desirable, due tomany factors, including the objections to handling a furnace of excessive height. Though there is no hard and fasst rule, it has been found by experiment that coil length very desirably approximates the diameter of the coil. On the other hand it may be ldesirable or necessary to melt or treat the metal in a shallow furnace, and'objects to be heated and not melted inquantlty suicient to justify the use of a special furnace ma be of much larger diameter or transverse 'mension than thelr length. Y

So far as I am aware,"in'the prior treatment of problems of this character the coil has been made in the form Of'a narrow band surrounding the Charge; and except for the resent invention it mi ht as well be in this Orm as an extension o the coil much below the charge would involve the inclusion within the ma etic circuit of an air gap of such length as, yfits reluctance, to more than offset the advantage to be gained by extension of the coil.A D v My invention contemplates the use of a lcoil appreciably ylonger than the .charge orcrucib e and the insertion of a ma eticcore within the space l'which would ot erwise be unoccupied by the charge in such an extension, iin order that themag'netizing current throughout the entire length of the coil may beefl'ective and will be required to drive the magnetic flux through an interior air gap but little more extendedl than the interior air P001- 01'/ gap which would be present in case of a short in Figure 1, a shallow furnace pool is shown 95 at 10 as enclosed within a refractory 11 which may or may not be a Crucible, and.Y forming either a furnace for meltingor additional heating, Ora ladle-'or storage receptacle intended for retention of moltelrmetal duringl Y treatment. i

About the pool and extending considerably b elow the limits of the pool I showan inductor 12 whose upper portion only is opposlte the pool. Under normal prior conditions of construction, if use of such a coil had been l'attempted the- 'lower portion ofthe' coil would have presented an open center 13. of`

high reluctance to the passage of magnetic k,flux caused by the magnetizing current in the cross-section, desirably correspondlng gen'v .of magnetic lines vertic coil and necessitating travel ofy the lines of force up and down the full length of the coil within it'and down and up the full length outside of the coil to complete the return magnetic circuit of the coil.

Within this spaceV 13 I place a magnetic core 14 llaminated along vertical lines, as

shown at 15, in order to freely allow assage ally through t e magnetic core in this space. J

The magnetic core may -be of any desired erally to the cross-sectionl of the space and vproviding a-suifcient cross-section of mag'- netic material for proper passage of the magnetic linesgthrough the core. This space may be ventilated or cooled if desired. Y

I am thus enabled to make the coil as long' and the cross-section of' the individual turn as great as I desire while confining the 'internal coreless length substantially to the length 7'of the Acharge or of the/charge and bottom refractory.

lsas

lIn Figure 1 nov assistance is givenv to the return, of .the external lines and the relucltance of this part of the magnetic circult is increased approximately in `proportion to the I increasein the length of the'coil.

In Figure 2 an external magnetic circuit is provided through laminated strips 16 of magnetic material extending alon the coil parallel `with its axis and inwar y turned beneath the core 14. Except as access to the top of the charge or' pouring may interfere the Kstrips' may be-turned in correspondingly at their upper ends. Instead ofthe stri s an auxiliary coil 17 can be usedtoelimmate Y' Y stray field outside of itand to assist the re- A turn magnetic circuit between it and the in ductor coil as in Figure 3, where two turns are shown.

'Where' an auxiliary coil is used it can be short-circuited or operated in series with the magnetic flux in the strips corresponding in' direction and preferably approximately in 'strength to the flux caused in them by inductor coil.

This approximates a condition of zero reluctance for the return 'line-s, helping the power factor and eliminating stray external field.y

In Figure 3 where coil 17 is shown and the strips are omitted, the coil is effective to eliminate external field beyond it but is not so effective to improve the power factor. IIowever,'this makes little difference because the power factor: correction can be taken care ofb condensers.

T e current through the coils should be in phase with the inductor current and may be in series with it as' shown.l

By my invention I am able to reduce the percentage of heat loss in inductor coils, par- -ticularly where the charge is of large diameter and of shallow depth, without sacrificing the 'advantages of external field elimination and return magnetic circuit ower factor improvement whichmay be app ied to the existing inductor coils. 4

The voltage Iused will be that suited for the inductor-and will nt'require adaptation to a special fiat inductor merely because the melt is of -low height.

In view of my invention and disclosure variations and modifications to meet individual whim or `particular need will doubtless become evident to others skilled in the art, to obtain all' or part of the benefits of my invention `without copying the structure shown, and I, therefore, claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is: p

1. Thefmethod of reducing the inductor heat losses in a .furnace inductor surrounding a charge free from interthreading of transformer iron) and much wider than its depth, which consists in increasing the axial length of the inductor much below the botvmuch wider than its depth, which consists in extending the inductor well .below the charge, providing a highly permeable path for magnetic lines within the inductor and below the charge, in roviding a magnetic return circuit for the ux from the inductor and in electro-magnetically setting up lines of. force inthe return circuit, asslsting the return magnetic flux from `the inductor through said magnetic material.

3. The method of reducing the losses of a furnace Ainductor surroundin a charge free from interthreading of trans ormer iron and much wider than its depth, which consists in extending the inductor well below the charge, in providing a highly permeable path. for magnetic lines in the space witmn the inductor and below the char and in providin ma etic assistance to t e return outside t e in uctor of the flux provided by the inductor.

4. The method of reducing the losses of a furnace inductor surroundin a charge free from interthreading of trans ormer iron and much wider than its depth, which consists in extending the inductor well below the charge, in providing a highly permeable path for magnetic lines Within the inductor and below the charge and in electro-magnetically assisting the return flux from the inductor outside of the inductor.

5. The method of reducing the losses of a furnace inductor surroundin a charge free from interthreading of trans ormer iron and much wider than its depth, which consists in' artificially extending the inductor below the charge for the purpose of obtaining desirable economy in furnace coil losses and in roviding a magnetic path for the additiona length of coil beneath the charge.

v6. An inductor furnace adapted for use about a charge free from interthreading of transformer iron and of considerably larger dimensions across the furnace than longitudinally of it, having an inductor coil about the charge extending much below the charge and va core of magnetic material within the extension of the coil beneath the charge.

7. An inductor furnace adapted for use about a char e free from interthreading of transformer lron and of considerably larger dimensions across the furnace than longitudinally of it, having an inductor coil of length not much less than its diameter and approximately on a level at its top with the top of the charge and a magnetic core within the coil and-beneath the charge and, from l side to side, substantially filling the coil.

8. An inductor furnace adapted for use about la charge free from interthreading of transformer iron and of considerably larger dimensions across the furnace than longitudinally of it, having an inductor coil surrounding the charge considerably longer than the depth of the charge and having its extension chiefly below the charge and a magnetic core within the coil beneath the charge and providing room for cooling ventilation between the core and the charge.

9. An inductor furnace adapted forA usel about a charge lfree from interthreading of transformer iron and of considerably-larger dimensions across the furnace than axially of it, an inductor coil considerably longer than the depth of the charge, surrounding the charge and having its extension chiefly beneath the charge and a magnetic core within the coil extension beneath the charge and having Ventilating passageways along the core longitudinally of the coil.

10. In an inductor furnace adapted to operate upon a shallow charge free from interthreading of transformer iron, a container for the charge, an-inductor coil having much greater length than the depth of the charge, eccentrically placed in an axial direction with respect to the charge to extend much 'more below the charge than above the charge and a magnetic circuit for said inductor assisting the magnetic lines Within the additional part of the inductor below the charge. I

11. In an inductor furnace adapted to 7;, operate `upon a shallow charge free from interthreadingI of transformer iron, a container for the charge, an inductor coil of much greater length than the depth of the charge having the upper part of the coil surrounding the charge, a core within the inductor below the charge and a magnetic return circuit for the llux caused by said inductor.

12. In an inductor furnace adapted to operate upbn a shallow charge free from interthreading of transformer iron, a container for the charge, an inductor coil :of much greater length than the depth of the charge having the upper part of the coil surrounding the charge, a core within the inductor below the charge and an electromagnetic return circuit for the flux caused by the inductor.

13. In an inductor furnace adapted to operate upon a shallow charge, a container for the charge, an inductor coil of much eater length than the depth of the charge aving the upper part of the coil surrounding the charge, a core within the inductor below the 100 charge and an electromagnetic return circuit for the flux caused by the inductor comprising magnetic material surrounded by a conductor carrying a current substantially in phase with the inductor current.

14. In an inductor furnace adapted to operate upon a shallow charge, a container for the charge, an inductor coil of much eater length than the depth of the charge aving the upper part of the coil surrounding the 11o charge, a core within the inductor below the charge and a conductor carrying electric current in phase with the inductor to set up lines of force outside of the conductor counter to those there set up by the inductor.

EDWIN FITCH NORTHRUP. 

